When is the last frost in Missoula, MT?

The average (50% probability) last spring frost in Missoula is May 16, based on NOAA 1991–2020 normals. A 1-in-10 risk remains until June 1.

When is the first frost in Missoula?

The average first fall frost in Missoula is September 26, with a growing season of about 130 days.

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Missoula, Montana frost dates

Average last spring frost: May 16. Average first fall frost: September 26. That gives a growing season of about 130 days. For frost-tender plants, a safer planting date is June 1, after which a freeze happens in only 1 year in 10.

Last frost (50%)

May 16

1-in-10 risk after Jun 1

First frost (50%)

Sep 26

1-in-10 risk before Sep 12

Growing season

130 days

median frost-free days

Hard freeze (28°F)

May 2

median last 28°F in spring

Frost risk by date

Chance of frost	Spring: frost after	Fall: frost before
90%	May 3	October 8
70%	May 10	October 1
50%	May 16	September 26
30%	May 22	September 20
10%	June 1	September 12

Read the spring column like this: there is a 10% chance of a 32°F freeze after June 1. These are NOAA probabilities for the Missoula International Airport weather station (USW00024153, elevation 973 m), 1991–2020.

Missoula vegetable planting calendar

Dates count from the 50% last-frost date (May 16). For tomatoes, peppers and other frost-tender crops, waiting until the 10% date (Jun 1) is the cautious choice.

Crop	Start seeds indoors	Plant out
Beans	Apr 25	May 23 (usually sown directly in the garden)
Broccoli	Mar 7	Apr 18
Brussels sprouts	Mar 7	Apr 18
Cabbage	Feb 28	Apr 11
Cauliflower	Mar 21	May 2
Sweet corn	Apr 18	May 16 (usually sown directly in the garden)
Cucumbers	May 2	May 23
Kale	Feb 28	Apr 11
Leeks	Jan 31	Apr 11
Lettuce	Mar 28	May 2
Melons	May 9	May 30
Onions	Jan 24	Apr 4 (from seed; sets and transplants go out at the same time)
Peas	Mar 21	Apr 18 (usually sown directly in the garden)
Peppers	Apr 4	May 30
Squash	May 9	May 30
Tomatoes	Mar 21	May 16

Offsets from Oregon State University Extension's seed-starting table. "Plant out" means transplant, or sow directly for crops usually grown from seed.

Fall frost and season extension

The first fall freeze usually arrives around September 26. There's a 1-in-10 chance it comes before September 12. Harvest tender crops such as basil, tomatoes, peppers and squash before then, or cover them on cold nights. Cool-season crops like kale, cabbage and Brussels sprouts handle light frost, and often taste sweeter after it. A hard freeze (28°F) typically comes around October 6.

Nearby cities

City	Last frost (50%)	First frost (50%)	Distance
Spokane, WA	Apr 26	Oct 12	~272 km
Boise, ID	Apr 24	Oct 21	~406 km
Billings, MT	May 4	Oct 7	~439 km
Yakima, WA	May 8	Oct 4	~491 km
Seattle, WA	Mar 2	Nov 23	~626 km
Portland, OR	Mar 13	Nov 19	~662 km

More: all Montana frost dates